Two shockwaves, measured at 3 Gs each, caught up with the plane, Van Kirk recalled.
The bomb detonated 43 seconds after it was dropped from the Enola Gay, as the pilot turned the plane away from the blast. Van Kirk, who also saw action in a B-17 in Europe and North Africa, described the Hiroshima mission as an easy one because the plane faced no enemy opposition and was flying in perfect weather. The first nuclear weapon used in warfare, Little Boy weighed 9,000 pounds and detonated 1,800 feet over Hiroshima with an explosive force that equaled 20,000 tons of TNT, according to the National Museum of the U.S. The plane carried Little Boy, the nickname for the first of two atomic bombs dropped over Japan - actions which forced Japan's surrender. "How they expected to tell you you were going out and dropping the first atomic bomb and it might blow up the airplane and go get some sleep, is absolutely beyond me," Van Kirk said in a video interview with the Witness to War Foundation. When their superiors advised them to get some rest after one of their last briefings, Van Kirk played poker with his crew mates instead. He had a lot on his mind the day before the mission. The city was home to 250,000 people, as well as an important army headquarters. Van Kirk served as the navigator for a crew of 12 aboard the Enola Gay, helping to guide the aircraft to Hiroshima on August 6, 1945.